Lubricating oil composition



United 4 States I are LUBRICATING OIL COMPOSITION Richard L. Ferm, El Cerrito, and Andrew D. Abbott,

Ross, Calif., assignors to California Research Corporatron, San Francisco, Calif., a corporation of Delaware No Drawing. Filed Mar. 31, 19 58, Ser. No. 724,820

4 Claims. (Cl. 252-323) bricating oil compositions to impart desirable viscositytemperature characteristics to the compositions. These additives are designed to modify lubricating oils so that changes in viscosity occurring with variations in temperature are kept as small as possible. Lubricating oils containing such polymeric additives are somewhat thickened at the'higher temperatures normally encountered in engine operation while at the same time retaining desirable low viscosity fluidity .at cold starting temperatures. The ability of a lubricating oil to accommodate increased temperatures with a minimum decrease in viscosity is indicated by its high Viscosity Index as derived from commonly accepted viscosity standards. Because of the aforementioned properties, these polymeric additives have been conveniently termed both (thickeners and viscosity index improvers.

Polymers of alkyl methacrylates are particularly effective additives of the above type. Included are polyalkyl methacrylates in which the alkyl groups are mixtures of lower alkyl groups of 7 carbon atoms or less and higher alkyl groups of 8 carbon atoms or more. Some of the more important polymeric methacrylates also provide enhanced detergent properties to mineral lubricating oil compositions as well as desirable viscosity-temperature characteristics. Among the more important polymeric viscosity index improvers and detergents of this type are the copolymers of the aforementioned alkyl methacrylates with monomers containing polar groups such as the N,N- dialkylaminoalkylmethacrylates, the polyglycolmonomethacrylates and the vinyl nitrogen heterocycles.

Mineral lubricating oils containing polymeric additives as described above are also commonly compounded with metal salt organic detergent additives. These metal salt additives alleviate the formation of undesirable engine deposits by giving the oil enhanced ability to maintain deposit-forming materials such as sludge and resins from oxidation in dispersion in the oil. Among the more important additives of this type are the essentially neutral alkaline earth metal petroleum sulfonates and the alkaline earth metal phenates or their sulfurized derivatives. Another important type of metal salt organic detergent additive, namely the zinc dithiophosphates imparts not only detergent characteristics but also oxidation and corrosion inhibiting properties to mineral lubricating oil compositions.

The two different classes of additives described above have been combined to give mineral lubricating oil compositions having excellent detergent properties along with superior viscosity-temparature characteristics. Unfortunately, it happens that the addition of the more important metal salt organic detergents to mineral lubricating oils containing the polymeric thickeners mentioned above has a decidedly adverse etfect on the viscosity-temperature characteristics of the mineral lubricating oil'compositions. There is an undesirable increase in the viscosity compared to the viscosity of the thickened mineral lubricating oil alone and the variations in viscosity with temperature changes of the oil are unfavorably exaggerated as indicated by the lowered viscosity index of the composition.

The above-mentioned adverse effect on the viscositytemperature characteristics of the mineral lubricating oil compositions is of the greatest importance inthe case of the so-called multigrade lubricating oils developed for more efiestive lubrication over the wide temperature ranges commonly encountered in internal combustion engines. Polymeric thickeners of the important polymethacrylate ester type are added to these oils to raise the viscosity index radically and thus enable a single oil to meet the specification viscosity ranges of two or three different SAE viscosity grades. The increase in viscosity, particularly at low temperatures where only certain viscosities can be tolerated, and the depreciation of the aforementioned critical viscosity index improvement of the thickened lubricating oil by the addition of the more important metal salt organic detergent additives referred to above may prevent an oil from qualifying as a multigrade oil.

The addition of the metal salt organic detergent additives to the thickened mineral lubricating oils has both an immediate adverse effect as described above, and also a postponed effect in that further undesirable increases in viscosity and depreciation of the viscosity index are observed over certain periods of time.

tremely critical since an otherwise satisfactory oil may become completely unsatisfactory during the usual storage periods for lubricating oils. i

.It has now been found that stable viscosity-temperature characteristics are provided in mineral lubricating oil compositions comprising a major portion of a mineral lubricating oil, a minor portion sufficient to improve the Viscosity index of the mineral lubricating oil of an alkyl- The mineral lubricating oil compositions of the invention possess unusually stable viscosity-temperature characwith carbonic acid. Suitable alkanediol teristics compared to mineral lubricating oil compositions containing polymethacrylate ester viscosity index improv ers in combination with metal salt organic detergent addi-' tives without the alkanediol carbonate. Particularly in the case of the multigrade lubrictaing oils where certain, minimum low temperature viscosities and minimum varia- 1 tions in viscosity of the oil over broad temperature ranges are critical, the outstanding properties of the compositions according to the invention are most appreciated." It

is found that the viscosity as well as theviscosityindex of the present compositions remains practically unchanged, even over extended periods of time. i The carbonates of alkanediols containing from 2 104 carbon atoms which are used in the lubricating oil'compositions of the invention are also commonly termed g g The are characterized. by. an' oma falkylene carbonates. v aliphatic hydrocarbon group of from to. 4 carbo having two hydroxyl groups attached which 'are This effect which i has been conveniently termed viscosity drift is exto 4 carbon 3 this class of compounds include ethane diol carbonate or ethylene carbonate, as it is commonly termed, 1,2- propane diol carbonate or propylene carbonate and 1,3- butanediol carbonate. For present purposes propylene carbonate is preferred since it provides the most viscosity stable compositions at lowest concentration.

The metal salt organic detergent additives of the more important types such as are employed in the mineral lubricating oil compositions according to the present invention include the neutral alkaline earth metal petroleum sulfonates, alkaline earth metal phenates, sulfurized alkaline earth metal phenates and zinc aromatic dithiophosphates as mentioned above. These particular metallo organic additives are generally recognized as efiective lubricating oil detergents and inhibitors and should require no particular description here. Illustrative alkaline earth metal petroleum sulfonates include barium petroleum sulfonate, calcium petroleum sulfonate, magnesium petroleum sulfonate and slightly basic calcium petroleum sulfonates having a base ratio not greater than 0.6 (base ratio being the ratio of basic calcium to total calcium). Only the substantially neutral sulfonates seem to have an adverse effect on the thickened mineral lubricating oils. Suitable alkaline earth metal alkyl phenates and sulfurized alkaline earth metal alkyl phenates include calcium cetylphenate. calcium tetradecylphenate, barium cetylphenate, and sulfurized calcium cetylphenate. The aforementioned phenates preferably contain from to 20 carbon atoms in the alkyl group and may be normal or basic in nature since both types alter the viscosity-temperature characteristics of the thickened oils undesirably. The zinc aromatic dithiophosphates of the compositions of the invention are characterized by the presence of at least one aryl group. Illustrative thiophosphates of this type include zinc dodecyl phenyl thiophosphate, zinc dihexylphenyl dithiophosphate, zinc hexyl naphthyl dithiophosphate and zinc diamylphenyl dithiophosphate. Thiophosphates without aryl groups do not appear to afiect the critical viscosity properties of the thickened compositions.

The polymeric methacrylate ester lubricating oil thickeners of the compositions according to the invention are also a recognized class of eifective lubricating oil additives. In general, they are polymers of higher alkyl esters of a,/8-unsaturated monocarboxylic acids of from 3 to 8 carbon atoms which contain oil-solubilizing alkyl groups of at least 8 carbon atoms. Illustrative esters of these types include dodecyl methacrylate, octadecyl methacrylate, tridecylacrylate and tetradecyl crotonate. The methacrylates are presently preferred since they provide very satisfactory improvement in the viscosity indexes of lubricating oil compositions. Other monomers, including lower alkyl methacrylates such as butyl methacrylate, may also be copolymerized with the aforementioned higher alkyl methacrylates. Polar monomers such as those characteristic of polymeric detergent additives for lubricating oils may also be included. These polymeric additives are also efiective viscosity index improvers as well as superior detergents. The more suitable polar monomers are the N,N-dialkylaminoalkyl methacrylates such as N,N-diethylaminoethyl methacrylate, the vinyl nitrogen heterocyclic compounds such as vinyl pyridine and vinyl pyrrolidone and the polyglycol monomethacrylates such as the dodecyl ether of octadecaethyleneglycol monomethacrylate.

Polymeric methacrylate viscosity index improvers of the above-mentioned types are generally characterized by molecular weights in the range of 100,000 to 300,000 and higher. In the case of the detergent polymeric compounds, the polar monomers are ordinarily present in proportions of from about 0.1 to about 35.0% by weight of the polymer.

The mineral lubricating oil of the lubricant composition of the invention may be any of the usual types of mineral lubricating base oils. Parafiinic or naphthenic base stocks are suitable. The mineral lubricating base oils may be refined by any of the conventional methods such as solvent refining or suifuric acid refining. Solventrefined Mid-Continent paraffinic-type base stocks appear to present the greatest viscosity stability problem and, therefore, have particular application to the compositions of the invention.

Further illustrations of the improved mineral lubricating oil compositions according to the present invention are provided by the following examples. Unless otherwise specified, the proportions in the examples are on a weight basis.

Several mineral lubricating oil compositions containing the typical polymethacrylate thickener-s referred to above and the metal salt organic detergent additives were prepared to show the effect of the metal salt additives on the thickened mineral lubricating oil compositions. In the compositions the base oil was a Mid-Continent paraffinic 200 neutral solvent refined mineral lubricating oil having a viscosity of 200 SSU at F. The oil was thickened with 6% by weight of the copolymer of a mixture of dodecyl methacrylate, octadecyl methacrylate, butylacrylate and N-vinylpyrrolidone in which there are approximately 65 parts by weight of the dodecyl and octadecyl methacrylates, approximately 25 parts by weight of butylacrylate and approximately 10 parts by weight of N-vinylpyrrolidone. The copolymer has an average molecular weight of approximately 150,000 to 200,000. Various metal salt detergent additives are added to the thickened mineral lubricating oil and the effect on the viscosity of the oil in Saybolt Seconds Universal (SSU) at 210 F. is observed as indicated in the following table. The proportions of the metallic salt detergent additives are given in millimoles per kilogram (mM./kg.).

Tetradecyl phenate derived from a mixture of propylene tetramer and pcntamer alkylated phenols having an average of approximately 14 carbon atoms in the alkyl group.

According to the above test results, it will be seen that the important metallic salt detergent additives of the alkaline earth metal petroleum sulfonate, alkaline earth meal phenate and zinc aromatic dithiophosphate types all have an adverse effect on the viscosity of the thickened mineral lubricating oil. The unusual nature of the viscosity stability problem shown by the above test data is emphasized by the fact that certain other metal salt detergent additives such as the zinc dialkyl dithiophosphates do not have any such adverse etfect on the viscosity of the thickened mineral lubricating oil.

The effect of the inclusion of a carbonate of an alkanediol containing from 2 to 4 carbon atoms in the thickened mineral lubricating oil compositions containing metal salt detergent additives in accordance with this invention is shown by a number of examples. Test results illustrating the viscosity-temperature characteristics of these examples are given in the following table.

Oil A in the table is the thickened oil described above consisting of a 200 neutral solvent-refined mineral lubrieating oil containing 6% by weight of methacrylate and vinyl pyrrolidene copolymer.

Oil B is the thickened oil plus 25 mM./kg. of calcium T) petroleum sulforiate (base ratio 0.4) .having' an average molecular weight of approximately 500.

Oil C is the thickened oil containing 35 mM./kg. of sulfurized calcium tetradecyl phenate (as previously described).

Oil D is a thickened oil consisting of 35% 100 neutral and 65% 200 neutral solvent refined mineral lubricating oil containing by weight of the copolymeric methacrylate thickener described above. The oil is compounded with 28 mM./kg. of calcium petroleum sulfonate (base ratio 0.4) having an average molecular weight of approximately 500, 6.5 mM./ kg. sulfurized calcium tetradecyl phenate (as previously described) and mM./kg. zinc butyl hexyl dithiophosphate.

.6 tives as will'be apparent to'th'os'e skilled in the'artf Ex:- pressed in numerical ranges, however, the polymeric thickening additives will be in the customary range of from 0.1 to 10.0% by weight of the composition. The

selected from the group consisting of alkylacrylates and alkylmethacrylates having alkyl groups containing from TABLE II Viscosity Viscosity Viscosity Viscosity Percent Oil at 0 F., at 210 F., Increase, Correction, Improvement SSU SSU 210 F., SSU 210 F., SSU

A-(Thickened Oil) 7,800 63.0 B-(Thiekened Oil+Meta1 Salt) 3,000 76.0 13.0 B-(Thickened Oi1+Metal Salt)+0.3% 1,2-propylene carbon 11, 200 69. 0 7. 0 54 C-(Thickened Oi1+Meta1 Salt) 14,500 80.0 17.0 C-(Thickened Oil-l-Metal Salt)+0.3% 1,2-propylene carbonat 12, 000 73. 0 7. 0 41 C-(Thickened Oil+Metal Salt)+0.3% Isooctyl Thloglynnlatn 13, 000 83. 0 3. 0 Negative In the above-described test results addition of alkanediol carbonate to the lubricating oil compositions is shown to overcome practically all the adverse efiect on the viscosity incurred by the addition of the metal salt to the thickened oil. The carbonated alkanediols of from 2 to 4 carbon atoms as exemplified by propylene carbonate are surprisingly better than other glycol esters in their improving ability.

Experiments were also carried out with the mineral lubricating oil compositions of the invention to illustrate the stability of their desirable viscosity-temperature characteristics over extended periods of time such as those encountered under normal storage conditions. A number of samples of thickened oils and metal salts, as described in connection with oil D above, were treated with varying amounts of 1,2-propylene carbonate. The results of these From the above test results it is seen that the mineral lubricating oil compositions containing polymeric thickener and metal salts have unstable viscosity-temperature characteristics during storage. The viscosities at 0 F. are undesirably high to begin with and become drastically worse with time. Furthermore, the Viscosity Index of such oils deteriorates badly with time.

By way of contrast, the same mineral lubricating oil compositions with l,2-propylene carbonate have consid-' erably improved viscosity-temperature characteristics. Both low temperature viscosity and the viscosity indexes of such compositions are stable throughout the extended period of days storage time.

In the foregoing description of the mineral lubricating oil compositions of the invention, the essential portions of the polymeric thickening additive, the metal salt and the alkanediol carbonate have been described as amounts suflicient to accomplish the obvious purposes of the addi- 4 to 6 carbonatoms each, (B) an ester selected from the group consisting of alkylacrylates and alkylmethacrylates having alkyl groups containing from 12 to 20 carbon atoms each and (C) vinyl pyrrolidone, said copolymer having a molecular weight in the range of 100,000 to 300,000 and said vinyl pyrrolidone being from about 0.] to about 35.0% by Weight of the copolymer, from 5 to millimoles per kilogram of a metal salt organic detergent additive selected from the class consisting of neutral alkaline earth metal petroleum sulfonate, alkaline earth metal phenate, sulfurized alkaline earth metal phenate and zinc aromatic dithiophosphate in which the aromatic groups are selected from the class consisting of alkylphenyl and alkylnaphthyl groups and from 0.05 to 1.0% by weight of propylene carbonate.

2. A lubricating oil composition comprising a major portion of a mineral lubricating oil,--from 0.1 to 10.0% by weight of an oil soluble copolymer of (A) an ester selected from the group consisting of alkylacrylates and.

alkylmethacrylates having alkyl groups in the range of 4 to 6 carbon atoms each, (B) an ester selected from the group consisting of alkylacrylates and alkylmethacrylates having alkyl groups in the range of 12 to 20 carbon atoms each and (C) vinyl pyrrolidone, said copolymer having a molecular weight in the range of 100,000 to 300,000 and said vinyl pyrrolidone being from about 0.1 to about 35.0% by weight of the copolymer, from 5 to 100 millimoles per kilogram each of neutral calcium petroleum sulfonate, sulfurized calcium tetradecyl phenate and zinc butyl hexyl dithiophosphate and from 0.05 to 1.0% by weight of 1,2-propylene carbonate.

3. A lubricating oil composition comprising a major portion of a mineral lubricating oil, from 0.1 to 10.0%, by

weight of an oil-soluble copolymer of (A) an ester selected from the group consisting of alkylacrylates and alkylmethacrylates having alkyl groups in the range'of 4 to 6 carbon atoms each, (B) an ester selected from the group consisting of alkylacrylates and alkylmethacrylates having alkyl groups in the range of 12 to 20 carbon atoms each and (C) vinyl pyrrolidone, said copolymer having a molecular weight in the range of 100,000 to 300,000

and said vinylpyrrolidone being from about 0.1 to about 35.0% by weight of the copolymer, from '5 to 1 00 milli fonate, and from 0.05 to 1.0% by weight of one carbonate.

4. A lubricating oil composition comprising a portion of a mineral lubricating oil, from 0.1 to 10.0% by weight of an oil-soluble copolymer of (A) an ester selected from the group consisting of alkylacrylates and alkylmethacrylates having alkyl groups in the range of 4 to 6 carbon atoms each, (B) an ester selected from the group consisting of alkylacrylates and alkylmethacrylates having alkyl groups in the range of 12 to 20 carbon atoms each and (C) vinyl pyrrolidone, said copolyrner having a molecular weight in the range of 100,000 to 300,000 and said vinyl pyrrolidone being from about 0.1 to about 35.0% by weight of the copolymer, from 5 to 100 millimoles per kilogram of sulfurized calcium tetradecyl phenate and from 0.05 to 1.0% by weight of 1,2-propy1ene carbonate.

References Cited in the file of this patent UNITED STATES PATENTS 1,907,891 Steimmig et a1 May 9, 1933 1,995,291 Carothers et a1. Mar. 26, 1935 2,263,265 Fincke et a1. Nov. 18, 1941 2,560,547 Bartleson July 17, 1951 2,602,048 Michaels et a1. July 1, 1952 2,718,504 Bartlett Sept. 20, 1955 10 2,833,719 Van Horne et a1. May 6, 1958 OTHER REFERENCES Ethylene Carbonate and Propylene Carbonate, Pub. by Carbide and Carbon Chemicals Co., 30 E. 42nd St., N.Y. 17, N.Y., page 3. 

1. A LUBRICATING OIL COMPOSITION COMPRISING A MAJOR PORTION OF A MINERAL LUBRICATING OIL, FROM 0.1 TO 10.0% BY WEIGHT OF AN OIL SOLUBLE COPOLYMER OF (A) AN ETSER SELECTED FROM THE GROUP CONSISTING OF ALKYLACRYLATES AND ALKYLMETHACRYLATES HAVING ALKYL GROUPS CONTAINING FROM 4 TO 6 CARBON ATOMS EACH, (B) AN ESTER SELECTED FROM THE GROUP CONSISTING OF ALKYLACRYLATES AND ALKYLMETHACRYLATES HAVING ALKYL GROUPS CONTAINING FROM 12 TO 20 CARBON ATOMS EACH AND (C) VINYL PYRROLIDONE, SAID COPOLYMER HAVING A MOLECULAR WEIGHT IN THE RANGE OF 100,000 TO 300,000 AND SAID VINYL PYRROLIDONE BEING FROM ABOUT 0.1 TO ABOUT 35.0% BY WEIGHT OF THE COPOLYMER, FROM 5 TO 100 MILLIMOLES PER KILOGRAM OF A METAL SALT ORGANIC DETERGENT ADDITIVE SELECTED FROM THE CLASS CONSISTING OF NEUTRAL ALKALINE EARTH METAL PETROLEUM SULFONATE, ALKALINE EARTH METAL PHENATE, SULFURIZED ALKALINE EARTH METAL PHENATE AND ZINC AROMATIC DITHIOPHOSPHATE IN WHICH THE AROMATIC GROUPS ARE SELECTED FROM THE CLASS CONSISTING OF ALKYLPHENYL AND ALKYLNAPHTHYL GROUPS AND FROM 0.05 TO 1.0% BY WEIGHT OF PROPYLENE CARBONATE. 